The current invention relates to the synthesis of unsaturated hydrocarbyl compounds such as alkenes from enamines via hydroboration.
Lewis et al., J. Chem. Soc. (B), 1969, 863 teach that enamines prepared from ketones can be subjected to hydroboration followed by hydrolysis in acetic acid to form the corresponding aminoboronic acid. The boronic acid, upon heating to reflux, undergoes elimination to produce the corresponding alkenes. Borane is taught to be useful as the hydroborating agent and generally the hydroboration is conducted at reduced temperatures.
Pasto et al., J. Org. Chem. 1966, 31, 2777 discuss the uncatalyzed, base catalyzed and acid catalyzed elimination reactions of organoboranes to form alkenes. The use of a mixture of tri-n-propylboron, di-n-propyldeuterioborane, mono-n-propyldideuterioborane and deuterioborane as a hydroborating agent is discussed.
Larson et al., Tetrahedron Letters, 1975, 4005 discuss the synthesis of alkenes via the hydroboration of cyclic trimethylsilyl enol ethers. The stereospecific synthesis of unsymmetrical cyclic alkenes is taught to be possible when single isomers of the trimethylsilyl enol ethers are available as starting materials.
The existing methods for the preparation of alkenes are not without problems. Problems include the limitations on the type of alkenes that may be prepared and the necessity of harsh reaction conditions. Thus, what is needed is a simple process for the preparation of alkenes that operates under mild conditions; that has applicability for the preparation of a wide variety of alkenes, both cyclic and acyclic; and that has utility for the preparation of stereospecific isomers.